The present invention relates to an alternating-current generator and, more particularly, to a three-phase alternating-current generator having a stator bundle with a center lamination. It also relates to a method of producing the center lamination of the stator bundle.
An alternating-current generator is known comprising a housing made of two end shields, a stator bundle with a center lamination received between the end shields and a rotor rotating in the stator bundle.
In alternating-current generators, and especially in three-phase generators such as dynamos for motor vehicles and the like, it is known (DE-OS 2 132 052) to construct the stator plate bundle with a center ring of greater diameter in such a why that this ring forms an outer annular flange for clamping the stator plate bundle between the two end shields of the generator. This ring is itself preferably a part of the stator plate, i.e. it is formed from one or more stator plate laminations which form the outer annular shape with their greater outer diameter for centering between the housing contact surfaces at both sides.
The stator center laminations are produced from one piece and are located between the two halves of the rest of the stator bundle. Further, it is preferable that eyes in the form of projections, e.g. four eyes, which serve as supporting surfaces for the end shields of the generator be uniformly distributed along the circumference of the center laminations. The entire stator bundle can then be riveted together and/or welded.
The eyes of the center laminations serving as centering means for the two end shields of the generator housing, which eyes are arranged along the circumference, make it possible to screw together the three structural component parts consisting of the A end shield, B end shield and stator bundle without the tightening forces of the screws guided through the eyes causing a deformation of the inner diameter of the stator. The two end shields in turn receive the bearing for the rotor shaft. In addition to efforts in other areas, it is necessary to support the rotor exactly in the center with respect to the stator to obtain a generator which is as quiet as possible. An important prerequisite for meeting this condition consists in that the center laminations of the stator bundle are aligned and placed between the remaining halves of the bundle in such a way that the coaxial deviation between the outer diameter of the center laminations and the inner diameter of the bundle as a whole is kept as small as possible. For this reason the center laminations must always be constructed in such a way that their outer diameter can be aligned so as to be exactly concentric to the inner diameter of the two remaining halves of the bundle.
The necessary degree of freedom for this is obtained in the center laminations, which are already necessarily constructed in one-piece for such an adjustment, in that the inner diameter of the center laminations is slightly greater than that of the two adjacent halves of the stator bundle; in other words, the inner diameter of the center laminations recedes slightly from the inner circle receiving the rotor. Further, the groove surfaces, i.e. the free surfaces remaining between the webs of the laminations, as well as the rivet hole diameter of the center laminations can be larger so that corresponding displacement is possible without leading to an overlapping of the areas of the stator bundle which are free as a result of the two halves of the bundle.
Obviously, the center laminations must therefore be in one piece or formed by a plurality of segments rigidly attached together, i.e. they cannot also comprise individual segments which can be loosely inserted into the bundle as is the case with the laminations forming the bundle halves which are known per se. This is because these segments would otherwise deflect inward due to the greater inner diameter of the center laminations during precise positioning in which the outer diameter is used as a point of reference.
However, one-piece laminations are very material-intensive, i.e. they require much base material since they must be stamped from a whole plate at considerable cost.
For this reason it is also already known (DE-PS 2 015 502) to produce annular laminations for electrodynamic machines by first starting from a planar plate of ferromagnetic work material and forming a pipe from this plate. This pipe is then cut into corresponding pipe pieces resulting in cylinders of given dimensions and with a thickness corresponding to the initial thickness of the plate. Every pipe piece is then made to bulge out between its end faces by a bulge deformation process and is then compressed by a force exerted in the axial direction to form a double-walled annular plate. During this compression of the bulged out pipe piece the inner and outer edges of the annular laminations formed in this way are simultaneously calibrated. It is then possible for the two laminations formed per se in every machining process to be separated from one another by undoing the bulged pipe piece at the outer edge. The grooves are then worked into the annular lamination at the inner edge. It is accordingly possible to produce laminations from one piece without wasting the entire inner plate of the lamination ring in the stamping process which is otherwise required. But it must be taken into account that the end face areas of the initial pipe piece must be given a smaller diameter and an average material layer must be given a greater diameter than the initial pipe diameter by the upsetting process, so that a flow of the material is necessary or different material thicknesses will result.